A novel high power x-ray tube having improved heat dissipation and compensation characteristics is shown and described in U.S. Pat. No. 3,842,305, assigned to the same assignee as the present invention. This tube comprises an evacuated envelope wherein a rotatable cup-shaped anode target has a sloped inner wall surface provided with an annular focal track from which x-rays are emitted when the track is bombarded by electrons.
The focal track comprises an annular channel in the sloped wall surface, which channel contains a plurality of pin-like target members disposed in side-by-side relation throughout the inner circumference of the target and extending parallel with each other in the direction of the width of the channel.
Disposed in operative spaced relation to a portion of the focal track is an electron emitting cathode from which electrons are electrostatically beamed onto the adjacent aligned portion of the focal track. As a result, the bombardment of the focal track by the electron beam causes the target members to emit x-radiation which passes out of the tube envelope through an exit window therein.
During operation of the tube, the anode is rotated, causing the target members to be sequentially moved through the electron beam. Thus, the heat generated by electron bombardment of the target members is distributed throughout the focal track and underlying body of the target.
The upper ends of the target members are, in known tube structures, interfitted beneath an overlying lip on the target body, and the lower ends are retained within the groove by a cup which is mounted by its base on the base of the target with its upwardly extending annular side wall being positioned in overlying relation to the lower edge of the groove and to the lower ends of the target members. Thus, the members are snugly retained in place within the groove, the dimensions of which are such that the members are permitted thermal expansion.
It will be apparent that during operation of the tube, centrifugal forces will urge the individual target members into close engagement with the bottom of the groove. This will aid in the transfer of heat from the members to the target body.
However, it has been found that dimension tolerances are critical and unless the parts of the device are precisely manufactured the target members may not properly engage the bottom of the groove for best thermal conductivity, or actually may become disengaged from the groove. Further, the inner retaining cup is fragile, usually being made of good thermal absorption material such as graphite, and is easily damaged or broken, thus possibly leaving particles in the tube which are detrimental to proper and efficient operation of the tube. The cup, still further, is a radiation barrier which often prevents complete outgassing during processing of the tube.